The present invention relates to a light-emitting element comprising a semiconductor multilayer film formed on an insulating substrate, to a semiconductor light-emitting device including such a semiconductor light-emitting element, and to manufacturing methods therefor. In particular, the present invention is properly applicable to a light-emitting element (LED) using a gallium-nitride-based compound semiconductor formed on a sapphire substrate and to a light-emitting device comprising such a light-emitting element.
As the demand for optical devices, such as liquid-crystal display devices, has grown in recent years, various light-emitting elements have found practical applications. Among them is a gallium-nitride-based compound semiconductor (InXAlYGa1xe2x88x92Xxe2x88x92YN, 0xe2x89xa6X, 0xe2x89xa6Y, X+Yxe2x89xa61), which is not only on the current market as a high-intensity blue and green light-emitting diode (LED) but also receiving attention as a prospective material for composing a blue laser diode, a UV sensor, and a solar cell in the future.
FIG. 4A is a plan view of a conventional GaN LED element which is commercially available. FIG. 4B is a cross-sectional view taken along the line Bxe2x80x94B thereof. FIG. 4C is a cross-sectional view taken along the line Cxe2x80x94C thereof. It is to be noted that the thickness of each semiconductor layer shown in the drawings does not necessarily coincide with the actual thickness thereof. FIG. 5 is a cross-sectional view of a conventional LED lamp which is commercially available. The GaN LED element 40 has a double heterostructure including a GaN buffer layer 31, an n-type GaN layer 32, an InGaN active layer 33, a p-type AlGaN layer 34, and a p-type GaN layer 35 which are stacked sequentially in layers on the top face of a sapphire substrate 30. The top face of the n-type GaN layer 32 has a stepped configuration consisting of an upper-level portion and a lower-level portion. An n-side electrode 36 made of Ti and Au is formed on the top face of the lower-level portion of the n-type GaN layer 32. The aforesaid InGaN active layers 33, the p-type AlGaN layer 34, and the p-type GaN layer 35 are stacked sequentially in layers on the top face of the upper-level portion of the n-type GaN layer 32. A transparent electrode 37 for current diffusion made of Ni and Au is formed on the top face of the p-type GaN layer 35, followed by a p-side electrode 38 formed thereon. Since the GaN LED element 40 is formed by using the insulating sapphire substrate, each of the two electrodes is formed on the top face of the sapphire substrate. The top face of the GaN LED element 40 serves as a light-emitting face, which is coated with a protective film 39 except for the bonding pad portions 36a and 38a of the n-side and p-side electrodes 36 and 38. The GaN LED element 40 is die-bonded to a die pad on the tip of a leadframe 44a via an insulating adhesive 43. The n-side electrode 36 of the GaN LED element 40 is connected to the leadframe 44a via an Au wire 41, while the p-side electrode 38 thereof is connected to a leadframe 44b via an Au wire 42. The respective tip portions of the leadframes 44a and 44b carrying the GaN LED element 40 are molded with a transparent epoxy resin 45 to constitute the LED lamp.
The foregoing conventional light-emitting element has the following problems.
To achieve wire bonding for providing an electrical connection between the GaN LED element 40 and another element or the like as described above, each of the bonding pad portions 36a and 38a should be configured as a circle having a diameter of 100 xcexcm or more or a square having sides of 100 xcexcm or more. Moreover, since the two electrodes 36 and 38 are formed on the light-emitting side, the light-emitting efficiency is degraded. If the bonding pad portions 36a and 38a are provided with a sufficiently large area and the light-emitting face is provided with a sufficiently large area for emitting a sufficient amount of light, the size reduction of the light-emitting element will be limited and the scaling down of the light-emitting element will be difficult.
It is therefore a primary object of the present invention to provide a semiconductor light-emitting element and a manufacturing method therefor, which enable a reduction in the area required by the electrodes to achieve electrical connection of the light-emitting element, the scaling down of the entire light-emitting element, and improvements in the brightness and light-emitting efficiency of the light-emitting element.
Another object of the present invention is to provide a light-emitting device comprising the aforesaid light-emitting element and a manufacturing method therefor.
A light-emitting element according to the present invention comprises: a substrate; a first-conductivity-type semiconductor region formed in the semiconductor substrate; a second-conductivity-type semiconductor region formed on a portion of the first-conductivity-type semiconductor region; a first electrode formed on a portion of the first-conductivity-type semiconductor region other than the portion in which the second-conductivity-type semiconductor region is formed; and a second electrode formed on the second-conductivity-type semiconductor region, the light-emitting element further comprising a plurality of microbumps made of a conductive material and formed on the first and second electrodes, wherein the number of the microbumps formed on the first electrode is one and the number of the microbumps formed on the second electrode is one or more.
Preferably, each of the microbumps has a columnar or mushroom-like configuration, a maximum lateral dimension ranging from 5 to 300 xcexcm, and a height ranging from 5 to 50 xcexcm.
Preferably, a metal layer having excellent adhesion to the first-conductivity-type or second-conductivity-type semiconductor region is provided under at least one of the first and second electrodes.
Another light-emitting element according to the present invention comprises: a substrate; a first-conductivity-type semiconductor region formed in the semiconductor substrate; a second-conductivity-type semiconductor region formed on a portion of the first-conductivity-type semiconductor region; a first electrode formed on a portion of the first-conductivity-type semiconductor region other than the portion in which the second-conductivity-type semiconductor region is formed; and a second electrode formed on the second-conductivity-type semiconductor region, the light-emitting element further comprising a plurality of microbumps made of a conductive material and formed on the first and second electrodes, each of the first and second electrodes having not only a region in which the microbump is formed but also a probe region to come into contact with a probe needle.
Preferably, the probe region of the first electrode is formed to extend over a part of a dicing street.
Still another light-emitting element according to the present invention comprises: a substrate; a first-conductivity-type semiconductor region formed in the semiconductor substrate; a second-conductivity-type semi-conductor region formed in a portion of the first-conductivity-type semiconductor region; a first electrode formed on a portion of the first-conductivity-type semiconductor region other than the portion in which the second-conductivity-type semiconductor region is formed; and a second electrode formed on the second-conductivity-type semiconductor region, the light-element further comprising a plurality of microbumps made of a conductive material and formed on the first and second electrodes, the second electrode including an opening for radiating light emitted from the light-emitting element to the outside.
Preferably, the opening formed in the second electrode is configured as a circle with a diameter of 20 xcexcm or less or as a polygon included in a circle with a diameter of 20 xcexcm or less.
A conductive transparent electrode may be provided in the opening formed in the second electrode to form an ohmic contact with the second-conductivity-type semiconductor region.
Preferably, the substrate is made of a material transparent to light radiated from the light-emitting element.
The substrate may be made of sapphire and a GaN-based compound semiconductor multilayer structure may be formed in the substrate.
The microbumps may be made of a metal material containing at least Au.
A method of manufacturing a light-emitting element according to the present invention comprises: a first step of forming, on a substrate, a semiconductor layer including at least a first-conductivity-type semiconductor region and a second-conductivity-type semiconductor region overlying the first-conductivity-type semiconductor region; a second step of partially removing the second-conductivity-type semiconductor region to expose a portion of the first-conductivity-type semiconductor region, a third step of forming a first electrode made of a first metal film on the portion of the first-conductivity-type semiconductor region; a fourth step of forming a second electrode made of a second metal film on a portion of the second-conductivity-type semiconductor region; a fifth step of forming a mask member having respective openings corresponding to a portion thereof overlying a part of the first electrode and to a portion thereof overlying a part of the second electrode; a sixth step of depositing a third metal film at least in the openings of the mask member; and a seventh step of removing the mask member and leaving the third metal film on the first and second electrodes to form microbumps.
Still another method of manufacturing a light-emitting element comprises: a first step of forming, on a substrate, a semiconductor layer including at least a first-conductivity-type semiconductor region and a second-conductivity-type semiconductor region overlying the first-conductivity-type semiconductor region; a second step of partially removing the second-conductivity-type semiconductor region to expose a portion of the first-conductivity-type semiconductor region; a third step of forming a first metal film on the portion of the first-conductivity-type semiconductor region; a fourth step of forming a second metal film over the entire surface of the substrate; a fifth step of forming a mask member having respective openings corresponding to a portion of the second metal film overlying a part of the first metal film and to a portion of the second metal film overlying a part of the second-conductivity-type semiconductor region; a sixth step of depositing a third metal film at least in the openings of the mask member; and a seventh step of removing the mask member and patterning the second metal film to leave, on the first-conductivity-type semiconductor region, a first electrode made of the first and second metal films and a microbump on the first electrode, while leaving, on the second-conductivity-type semiconductor region, a second electrode made of the second metal film and a microbump on the second electrode.
The sixth step may include depositing the third metal film by a selective plating technique.
A light-emitting device according to the present invention comprises: a light-emitting element including an insulating substrate and a semiconductor film formed on the insulating substrate, a p-type semiconductor region and an n-type semiconductor region being formed in the vicinity of a top face of the semiconductor film, the light-emitting element emitting light in response to a voltage applied between the p-type semiconductor region and the n-type semiconductor region; and an electrostatic protection element having first and second regions electrically connected to the p-type semiconductor region and to the n-type semiconductor region, respectively, the electrostatic protection element allowing current to flow between the first region and the second region when a voltage exceeding a specified value equal to or lower than a destruction voltage is applied between the p-type and n-type semiconductor regions of the light-emitting element.
Preferably, the electrostatic protection element is constituted such that current is more likely to flow in a forward direction from the first region to the second region than in a reverse direction from the second region to the first region and the p-type semiconductor region of the light-emitting element is electrically connected to the second region of the electrostatic protection element and the n-type semiconductor region of the light-emitting element is electrically connected to the first region of the electrostatic protection element.
Preferably, the electrostatic protection element is a diode.
Preferably, a forward operating voltage of the diode is lower than a reverse destruction voltage of the light-emitting element and a reverse breakdown voltage of the diode is higher than an operating voltage of the light-emitting element and lower than a forward destruction voltage of the light-emitting element.
The electrostatic protection element may be a field-effect transistor in which the first region is a drain region and the second region is a source region and a threshold voltage of the field-effect transistor may be equal to or higher than an operating voltage of the light-emitting element and equal to or lower than each of forward and reverse destruction voltages of the light-emitting element.
Preferably, the light-emitting element and the electrostatic protection element are overlapped each other.
Preferably, the electrostatic protection element is a diode in which current flows in a forward direction from the first region to the second region, the electrostatic protection element having first and second electrodes connected to the first and second regions, respectively, on one surface thereof, the light-emitting element has a p-side electrode connected to the p-type semiconductor region and an n-side electrode connected to the n-type semiconductor region on the top face thereof, and microbumps provide electrical connections between the p-side electrode of the light-emitting element and the second electrode of the electrostatic protection element and between the n-side electrode of the light-emitting element and the first electrode of the electrostatic protection element.
The light-emitting element may be mechanically connected onto the electrostatic protection element with an adhesive and at least one of the first and second electrodes of the electrostatic protection element may be divided into a region connected to the p-side or n-side electrode of the light-emitting element via the microbump and a bonding pad region connected to an external member via a wire.
The light-emitting element may be mechanically connected to the electrostatic protection element with an adhesive and the first and second electrodes of the electrostatic protection element as a whole may be made up of a plurality of rectangular portions divided in a direction.
The light-emitting element may be mechanically connected to the electrostatic protection element with an adhesive and a recess or a projecting portion may be formed to surround the region of the first and second electrodes of the electrostatic protection element in which the adhesive is present.
The light-emitting element may be mounted on the electrostatic protection element and either one of the first and second electrodes of the electrostatic protection element may be formed in the same region as a light-emitting region of the light-emitting element when viewed from above, light emitted from a light-emitting region being reflected upward.
The diode may be a lateral diode in which the first and second regions are p-type and n-type semiconductor regions each formed in a portion of a semiconductor region close to one surface thereof.
The electrostatic protection element may be made of a semiconductor thin film formed on the light-emitting element with an interlayer insulating film interposed therebetween.
The electrostatic protection element and the light-emitting element may be formed in the insulating substrate.
The electrostatic protection element may be made of a semiconductor thin film formed on the insulating substrate.
The insulating substrate of the light-emitting element and the electrostatic protection element may be provided on a single common base substrate.
The electrostatic protection element may be made of a semiconductor thin film formed on the base substrate.
The light-emitting element may be for use as a back light of a liquid-crystal device.
Preferably, the light-emitting element and the electrostatic protection element are accommodated in a single common house.
Preferably, a reflector is further provided at least around the light-emitting element to reflect light emitted from light-emitting element.
The reflector may have an upper end higher in level than a light-emitting region in the light-emitting element.
Preferably, the reflector is formed of a metal lead and the electrostatic protection element is mounted on the metal lead.
Another light-emitting device according to the present invention comprises: a GaN-based compound light-emitting element having an insulating substrate and a GaN-based semiconductor layer formed in the insulating substrate; and an electrostatic protection element for protecting the GaN-based compound light-emitting element from static electricity.
Preferably, the electrostatic protection element is made of a diode element having a p-side electrode and an n-side electrode and the p-side electrode of the diode element is electrically connected to an n-side electrode of the GaN-based light-emitting element and the n-side electrode of the diode element is electrically connected to a p-side electrode of the GaN-based light-emitting element.
Preferably, microbumps provide the connection between the p-side electrode of the diode element and the n-side electrode of the GaN-based light-emitting element and the connection between the n-side electrode of the diode element and the p-side electrode of the GaN-based light-emitting element to constitute a composite device of an electronic device and an optical device.
Preferably, the GaN-based light-emitting element and the electrostatic protection element are incorporated in a single common house.
A method of manufacturing a flip-chip semiconductor light-emitting device according to the present invention comprises: a semiconductor light-emitting element having a semiconductor multilayer film formed on a transparent substrate and p-side and n-side electrodes formed on a surface of the semiconductor multilayer film; a submount element having at least two independent electrodes; and a base capable of supporting the submount element and supplying electric power to the submount element, the submount element being mounted on the base to be electrically conductive to the base, the semiconductor light-emitting element being mounted in a face-down configuration on a top face of the submount element, the manufacturing method comprising: a microbump forming step of forming microbumps on the electrodes of either one of the semiconductor light-emitting element and the submount element; and a chip bonding step of bonding the p-side and n-side electrodes of the semiconductor light-emitting element to the electrodes of the submount element via the microbumps.
The chip bonding step may include the steps of: bringing the semiconductor light-emitting element in the form of a chip closer to a wafer, in which a plurality of submount elements, including the submount element arranged in rows and columns, are formed; and bonding the p-side and n-side electrodes of the semiconductor light-emitting element to the respective electrodes of the submount element formed in the wafer via the microbumps, after the chip bonding, the manufacturing method further comprising the step of separating the wafer into individual chips and forming, from the wafer, plural pairs of the semiconductor light-emitting elements and the submount elements integrated with each other.
The chip bonding step may include the step of applying heat, ultrasonic waves, or load to at least one of the semiconductor light-emitting element and the submount element, while bringing the electrodes opposed to each other into contact with each other via the microbumps, and thereby welding the microbumps to the electrodes.
The microbump forming step may include the step of forming stud bumps onto the p-side and n-side electrodes of the semiconductor light-emitting element and the chip bonding step may include the steps of: aligning the corresponding semiconductor light-emitting element with respect to each of the submount elements in the wafer, and welding the microbumps to the electrodes of each of the submount elements in the wafer to fix the semiconductor light-emitting element onto the submount element and provide mutual electric connections between the opposed electrodes via the microbumps, the manufacturing method further comprising the step of separating, from the wafer, the pairs of the semiconductor light-emitting elements and the submount elements integrated with each other, placing each of the pairs on a mount portion of the base, and fixing the submount element onto the base.
The microbump forming step may include the step of forming stud bumps on the p-side and n-side electrodes of the semiconductor light-emitting element and the chip bonding step may include the step of disposing the submount element on a mount portion of the base, fixing the submount element onto the base, and welding the microbumps to the electrodes of the submount element to fix the semiconductor light-emitting element onto the submount element and provide mutual electric connections between the opposed electrodes via the microbumps.
The microbumps may be formed by a plating process.
The microbump forming step may include the step of forming stud bumps onto the electrodes of each of the submount elements formed in the wafer and the chip bonding step may include the step of aligning the corresponding semiconductor light-emitting element with respect to each of the submount elements in the wafer and welding the microbumps to the electrodes of the semiconductor light-emitting element to fix the semiconductor light-emitting element onto the submount element and provide mutual electric connections between the opposed electrodes via the microbumps.
The microbump forming step may include the step of forming stud bumps on the electrodes of the submount element and the chip bonding step may include disposing the submount element on a mount portion of the base, fixing the submount element onto the base, and welding the microbumps to the electrodes of the semiconductor light-emitting element to fix the semiconductor light-emitting element onto the submount element and provide mutual electric connections between the opposed electrodes via the microbumps.
The microbumps may be formed by a plating process.
After the chip bonding, there may further be performed an optical-characteristic testing step of bringing a probe needle into contact with the submount element and thereby testing light radiated from the semiconductor light-emitting element from above a top face of the transparent substrate by using a detector for an optical characteristic test positioned above the semiconductor light-emitting element.
The chip bonding step may include the steps of: bringing the semiconductor light-emitting element in the form of a chip closer to the wafer, in which the plurality of submount elements, including the submount element arranged in rows and columns, are formed; and bonding the p-side and n-side electrodes of the semiconductor light-emitting element to the respective electrodes of the submount element formed in the wafer via the microbumps.
Preferably, the optical-characteristic testing step is performed with respect to each of the semiconductor light-emitting elements in the wafer after the chip bonding.